In the injection molding field, the volumetric variation of the plastic material directly affects the curvature and the shrinkage of the product. Normally, the volumetric variation of the plastic material is influenced by temperature and pressure during an injection molding operation. Therefore, it is important to understand relationships among the specific volume, temperature and pressure of the plastic material during the injection molding operation.
A conventional measuring apparatus for measuring the volumetric variation of the plastic material includes a base and a testing module. The testing module is received in the base and includes a bucket, a testing cylinder received in the bucket and receiving a testing sample, a heating unit connected to the bucket, and a piston plugging the testing cylinder. During a measuring operation, the density of the testing sample may lack uniformity due to non-uniform temperature distribution, and measurement errors may occur as a result. In addition, the non-uniform temperature distribution may also lead to interference between the piston and the testing cylinder. As a result, the piston may become jammed in the testing cylinder, or the testing sample may leak through a gap between the piston and the testing cylinder.
This Discussion of the Background section is for background information only. The statements in this Discussion of the Background are not an admission that the subject matter disclosed in this section constitutes a prior art to the present disclosure, and no part of this section may be used as an admission that any part of this application, including this Discussion of the Background section, constitutes prior art to the present disclosure.